Communication systems of scrambling/descrambling data subject to transmission with a view to preventing the same data patterns from being repeatedly produced in transmission data, etc. for encrypting data subject to transmission, and/or realizing improvement in disturbance (interference) proof characteristic, etc. are widely employed in various communication systems. In order to use such scramble/descramble system, it is necessary to realize matching between data exerted for the purpose of performing scramble processing in transmitting unit and data exerted for performing descramble processing in receiving unit, i.e., to take synchronization between the transmitting unit and the receiving unit with respect to arbitrary data subject to transmission. As a method of taking synchronization, there are used a method of prescribing scramble pattern (descramble pattern) in advance, etc., and/or a method of performing transmission of information for prescribing scramble pattern in the state where those information are disposed (assigned) at predetermined positions of transmission data, etc.
Particularly, in using the scramble/descramble system for preventing the same data patterns from repeatedly taking place within transmission data, there are many cases where widely used PN series are used as scramble pattern.
FIG. 1 is a view showing one example of a data scrambler adapted for outputting PN series. In FIG. 1, reference numeral 101 indicates a shift register of 4 (four) bits, reference numeral 102 indicates a shift register of 3 (three) bits, reference numeral 103 indicates a modulo-2 adder supplied with bit data X7 and bit data X4 to perform Exclusive OR (hereinafter referred to as EXOR) operation, and reference numeral 104 indicates a modulo-2 adder supplied with output data of the adder 103 and data subject to scramble (descramble) processing to perform EXOR operation. In addition, output data of the adder 103 is inputted to the shift register 101, and output data of the shift register 101 is inputted to the shift register 102. Namely, a shift register of 7 (seven) bits operative to sequentially shift output data of the adder 103 is composed of the shift register 101 and the shift register 102. When such a configuration is employed, the data scrambler shown in FIG. 1 outputs random bit data train at period of 127 (27-1) bits thus to operate as pseudo-random number generating circuit.
In performing scramble/descramble system by using data scrambler which outputs PN series in a manner as described above, there is used data scrambler as shown in FIG. 1 which essentially has the same configuration as scrambler ordinarily provided at transmitting unit and descrambler ordinarily provided at receiving unit. The scrambler and the descrambler are caused to be of the same configuration, thereby making it possible to relatively easily construct self-synchronization type communication system which includes information for prescribing scramble pattern into transmission data to thereby take synchronization between the transmitting unit and the receiving unit. In view of the fact that, e.g., EXOR operation value according to bit data X and “0” results in bit data X itself, communication system is controlled such that “0” (zeros) are successively inputted by a predetermined number of bits with respect to the scrambler, and scrambler output data are sequentially outputted to a shift register having a predetermined number of bits which is provided within descrambler. Thus, the same bit data are sequentially and successively inputted, by a predetermined number of bits, to the shift register having a predetermined number of bits which constitutes the scrambler and the shift register having a predetermined number of bits which constitutes the descrambler. From this fact, after “0” are successively inputted to the scrambler by a predetermined number of bits, the same bit data trains are respectively stored into the shift register of the scrambler and the shift register of the descrambler. Thus, synchronization is taken (established) between the transmitting unit and the receiving unit.
FIG. 2 is a view showing the configuration of a conventional descrambler. It is to be noted that since common reference numerals are respectively attached to components common to those of FIG. 1 in FIG. 2, the detailed explanation thereof will be omitted.
In FIG. 2, reference numeral 105 indicates a switch supplied with data inputted to the descrambler and output data from the adder 103 to selectively output either one of data to the shift register 101. The switch 105 performs switching control so that transmission data inputted to the descrambler is inputted to the shift register 101 for a time period during which there is performed transmission of data obtained as the result of the fact that “0” successive by 7 (seven) bits are inputted to the scrambler to perform scramble processing with respect to the data. In this instance, output data of the scrambler respectively obtained with respect to “0” of 7 (seven) bits inputted to the scrambler, i.e., output data of the adder 103 within the scrambler are sequentially inputted to the shift register 101 of the descrambler. Thus, at the time point when output data of the scrambler with respect to “0” of the seventh bit is inputted to the shift register 101 of the descrambler, bit data train stored into the shift register of 7 (seven) bits within the scrambler and bit data train stored into the shift register of 7 (seven) bits within the descrambler are equal to each other. Thus, synchronization is taken (established). Thereafter, the switch 105 is switched so that data outputted from the adder 103 is inputted to the shift register 101. After synchronization is taken, the same scramble pattern is exerted, in the scrambler and the descrambler, on data subject to transmission. Accordingly, data transmission using the scramble/descramble system is performed.
Meanwhile, in IEEE802.11 given as standard for the purpose of realizing standardization according to packet transmission of wireless LAN, etc., it is prescribed that there should be employed the configuration adapted for successively inputting “0” by a predetermined number of bits to the scrambler at the header portion of packet in order to synchronize the descrambler of the receiving unit with the scrambler of the transmitting unit. FIG. 3 is a view showing frame structure prescribed in the IEEE802.11. In FIG. 3, “PCLP Preamble” field is used for taking frame synchronization, “SIGNAL” field is used for notifying transmission speed and/or modulation system, etc., and “SERVICE” field is used for synchronizing the descrambler with the scrambler. In “SERVICE” field, “Scrambler Initialization” consisting of the first half 7 (seven) bits all take values of “0” in order to take (establish) synchronization between the scrambler and the descrambler. Moreover, with respect to “Reserved SERVICE Bits” consisting of the latter half 9 (nine) bits, its use is reserved at present in anticipation of future use. With respect to frame data generated in conformity with the IEEE802.11, the scrambler as shown in FIG. 1 and the descrambler as shown in FIG. 2 are used to perform, as occasion demands, various controls according to output switching of transmission data inputted to the descrambler in accordance with “Scrambler Initialization”, etc. to thereby establish synchronization between the scrambler and the descrambler. It is to be noted that, with respect to the technology according to the scramble/descramble system using PN series, there is a technology described in. e.g., the Japanese Patent Application Laid Open No. 1996-204613 publication.
As described above, in the communication system in conformity with the IEEE802.11 in which employment with respect to communication system of broad category is expected in future, it is prescribed that “0” of a predetermined number of bits are successively outputted to the scrambler of the transmitting unit at predetermined positions within frame in order to take synchronization between the scrambler and the descrambler. For this time period, data obtained by performing scramble processing with respect to “0” are transmitted from the transmitting unit to the receiving unit. However, there is the problem that when transmission data for synchronization outputted from the transmitting unit is compared with data caused to undergo transmission by using ordinary data field, although such transmission data is data having predominance which can endow various attributes on the basis of the fact that positions on the frame are established, there is failure or lack in effective utilization of data as the communication system because there is no possibility that such transmission data are used except for establishing synchronization.